How much house insulation is enough?

  • Active since 1995, Hearth.com is THE place on the internet for free information and advice about wood stoves, pellet stoves and other energy saving equipment.

    We strive to provide opinions, articles, discussions and history related to Hearth Products and in a more general sense, energy issues.

    We promote the EFFICIENT, RESPONSIBLE, CLEAN and SAFE use of all fuels, whether renewable or fossil.

Propane_Poor

Member
Oct 20, 2018
75
Ohio
We added a 1000 sqft to our 900 sqft 1960s house. All single story on crawl. Added 2" foam board to inside of the crawlspace blocks. R13 in the walls. R30 in the ceiling. The old section had old insulation probably also r13, some loose ceiling installation, and a very cold crawlspace, and was very drafty.

I should have pushed for r15 or r19 in the walls. It's too late to do more in the walls but I'm wondering if I should do more in the ceilings?

Also wondering if I should do the underside of the floor between the joists, in both the old and new sections?

The new section will take the brunt of the west wind.

The plan is to heat entirely with our BK Ashford 30.2.
 

EbS-P

Minister of Fire
Jan 19, 2019
3,510
SE North Carolina
I’m about to add R30 batt to my attic. It has prob 6” of old loose fiberglass. But before that I’m going to buy a case of great stuff foam and a case of the cheapest caulk and air seal everything. Not stopping until i’ve used all of it. All ceiling and exterior wall penetrations. I will finish replacing all switches and receptacles and install the foam gasket on all the outlets.

Before I lay down the batts I will try and seal every top plate.

Downstairs I caulked around ever ceiling fixture where the j box meets the sheet rock. Some boxes I can’t get to from the attic to to an attic floor so I’m doing my best from the bottom.

Remember doubling the amount of insulation does not cut the heat flow in half. So there is a point where you will not recover your financial investments. Code here for attic is r38. I’m shooting for r45-50. And considering adding radiant barrier under roof joists. So I’d shoot for at least r14 over code for attic.

I watched this video recently. Matt had deep pockets and really build for the south but I find this video to be more general. It convinced me to get a blower door test.
 
  • Like
Reactions: stoveliker

stoveliker

Minister of Fire
Nov 17, 2019
6,165
Long Island NY
Yes, add more in the attic. But first air seal the ceiling.

I did that, went from R19 to R 48 or so, after air sealing. Made a huge difference.
 

Propane_Poor

Member
Oct 20, 2018
75
Ohio
Yes, add more in the attic. But first air seal the ceiling.

I did that, went from R19 to R 48 or so, after air sealing. Made a huge difference.
How do you air seal the ceiling? Are you referring to the attich not being airtight or the gaps between the ceiling and the attic?
 

stoveliker

Minister of Fire
Nov 17, 2019
6,165
Long Island NY
How do you air seal the ceiling? Are you referring to the attich not being airtight or the gaps between the ceiling and the attic?
Go in the attic, locate all ceiling penetrations (lights, exhaust fans etc.) and use silicone caulk to seal the seams between them and the drywall of the ceiling. No spray foam that might expand in electrical boxes (fire hazard). Note many electrical boxes have holes in themselves too that need sealing with caulk.

Be aware of any heat producing can lights. There are rules about what to do there; don't want to overheat them. I had none, so I don't know.

Then on any top plate (horizontal 2*4 on top of a wall, be it internal or external wall), you'll see gaps between the (vertical) drywall and the top plate. Heat goes thru the drywall (and electrical outlets in the wall!!) and travels up, exiting thru those 1/8" gaps. Add all those gap strips up and you have one gaping hole into your attic. That is where canned spray foam is used.

Note where electric wires go down thru the top plate; big hole. Seal that too.

Then add weather stripping to the attic hatch, and insulation above. (Buy package or finagle yourself.)

Finally, add insulation.

Note that for all these steps, a lot of insulation needs to be moved to access sealing points.

Finally switch off all electric, take off all plates from switches and outlets in all walls (int. and ext.), and silicone the hopes in the box, and add a foam layer (buy at box store) under the plates.
 

EbS-P

Minister of Fire
Jan 19, 2019
3,510
SE North Carolina
If you have pull down attic ladder i wether stripped glued foam board under behind the steps weather stripping then added one of these. It’s probably not doing much but it’s something

GCGOODS Attic Stairs Insulation Cover 25" x 54" x 11", Attic Door Insulation Covers, Attic Stairway Insulated Tent with Easy Zipper Access, Energy Saver Attic Ladder Insulation Cover https://a.co/d/1lB63xr
 

stoveliker

Minister of Fire
Nov 17, 2019
6,165
Long Island NY
For the attic hatch, I put conventional weather stripping where it seals, and given that I added R38 batts (unfaced) on top of the existing R19 that was between the joists, I built a "enclosure" out of plywood and scrap lumber to hold the thicker insulation out of the hole of the hatch.

Then in that enclosure I screwed horizontal 2*2s creating a ledge onto which I lay the following.

I bought 2" thick pink foam boards, cut them to size to fit on the ledges, glued two of them to each other (forgot the r value), and glued remaining R 38 scrap batts on the board. That fits snug on the ledges.

So, I open the (air sealed because weather stripped) hatch, and I lift the foam+batt insulation "lid" out into the attic, and then I climb in. The whole thing weighs less than 2 lbs.

If it's winter and the attic is 20 F (as outside), and I open the hatch, no cold is coming down at all. So it works.

That's my R48 insulated attic hatch. (Assuming the boards are both R5.)
 

stoveliker

Minister of Fire
Nov 17, 2019
6,165
Long Island NY
Essentially, you have to air seal and insulate. Don't forget one of them. In tandem they work good. Alone, it's a lot of effort for small returns.
 

peakbagger

Minister of Fire
Jul 11, 2008
7,679
Northern NH
I agree that you are probably far past the point where you should be concentrating on insulation until you spend time on air infiltration. The proper was to do it is with a blower door test. The blower door drops the air pressure inside the house so that leaks are magnified and also by measuring the pressure drop can calculate how much air is leaking in. Then the leaks are identified with smoke gun and sealed. The blower test is then repeated until a target air flow is obtained. No one would try to heat a house with hole in the wall but that is what air infiltration does, its just split up all over the place in hard to see spots.

One of the issues with standard framing is that with thicker insulation the actual studs in the walls start to conduct a lot of heat relative to the insulation. If an IR gun is used the studs will become very noticable. When I renovated and interior wall I put a sheet of Isoboard foil faced foam on top of the studs and under the drywall. It made quite a difference.

My guess is you are going to find some big surprises on the air infiltration sealing. Bathroom fans have crappy backflap dampers that usually stick in the open direction and kitchen hoods are also really bad.

Once you get the building tight, then you can play with a on line manual J heating calculator and see what insulation changes gives you the best bang for the buck.

BTW windows are notorious for heat loss. If you can cover them in the winter it can make a big difference. Double cellular blinds with side seals will possibly double the R value. They still transmit quite a bit of light into the room and open and close quickly if you want the view.
 

Highbeam

Minister of Fire
Dec 28, 2006
19,986
Mt. Rainier Foothills, WA
I don’t know how they do it in NY but here the drywallers install the ceiling lid rock first which of course can’t be perfect so you’ll see that 1/8” gap around the edge but then they install the walls and screw that to the side of the top plate. I doubt it’s perfect but the gap you see in the attic is not the same size gap that leads into the wall cavity.